A reducing agent contains thiourea dioxide, for example. The thiourea dioxide having a reducing ability is used in a discharge printing agent, a bleaching agent, or a deinking agent, for example.
In the case where thiourea dioxide is used in a reducing agent, it is required to dissolve the thiourea dioxide in water. However, the solubility of the thiourea dioxide in water is a few wt % which is low. Since the reducing agent may only contain little amount of thiourea dioxide relative to the total amount of the reducing agent, there is a possibility that the reducing ability is low when the thiourea dioxide is used alone as a reducing agent.
Thiourea dioxide is hydrolyzed in an aqueous solution over time, and the concentration thereof is reduced. Accordingly, the reducing ability of thiourea dioxide is reduced over time. For example, when thiourea dioxide is used in a discharge printing agent, the discharge printing effect is maintained only for a short period of time such as about a few weeks. Thus, for example, there is a problem in that the discharge printing ability is reduced when the reducing agent containing thiourea dioxide is stored for a long period of time such as a few months.